fix: Strip UTF-8 BOM from resources to prevent corruption in XML and properties files

[d3xter666]

JIRA: CPOUI5FOUNDATION-1364
Resolves: #1601

Additionally JSON & HTML files saved with UTF-8 BOM were fixed, too

[d3xter666]

The return values of _calcMinSize in packages/builder/lib/lbt/bundle/AutoSplitter.js are now consistent: every branch returns a character count (String.length), matching how BundleWriter measures the generated bundle. Previously the method mixed byte counts (Buffer.length) and character counts across its branches. See b9c76d7.

This is a minor cleanup rather than a bug fix. _calcMinSize only produces an approximate size that is used to balance modules across split bundles, so a few characters more or less has no functional impact. I noticed the inconsistency while implementing the BOM stripping and decided to align it.

If the mixed units were intentional for some reason, let me know and I'll drop this part.

[matz3]

Remark about AutoSplitter.js changes. Everything else LGTM.